[PATCH 06/16] x86/reboot: KVM: Disable SVM during reboot via virt/KVM reboot callback

From: Sean Christopherson
Date: Thu Dec 01 2022 - 18:27:52 EST


Use the virt callback to disable SVM (and set GIF=1) during an emergency
instead of blindly attempting to disable SVM. Like the VMX case, if KVM
(or an out-of-tree hypervisor) isn't loaded/active, SVM can't be in use.

Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
arch/x86/include/asm/reboot.h | 2 +-
arch/x86/include/asm/virtext.h | 8 --------
arch/x86/kernel/reboot.c | 6 ++----
arch/x86/kvm/svm/svm.c | 19 +++++++++++++++++--
4 files changed, 20 insertions(+), 15 deletions(-)

diff --git a/arch/x86/include/asm/reboot.h b/arch/x86/include/asm/reboot.h
index 1d098a7d329a..dc2b77e6704b 100644
--- a/arch/x86/include/asm/reboot.h
+++ b/arch/x86/include/asm/reboot.h
@@ -25,7 +25,7 @@ void __noreturn machine_real_restart(unsigned int type);
#define MRR_BIOS 0
#define MRR_APM 1

-#if IS_ENABLED(CONFIG_KVM_INTEL)
+#if IS_ENABLED(CONFIG_KVM_INTEL) || IS_ENABLED(CONFIG_KVM_AMD)
typedef void (cpu_emergency_virt_cb)(void);
void cpu_emergency_register_virt_callback(cpu_emergency_virt_cb *callback);
void cpu_emergency_unregister_virt_callback(cpu_emergency_virt_cb *callback);
diff --git a/arch/x86/include/asm/virtext.h b/arch/x86/include/asm/virtext.h
index 4f61283b1f52..97349410c937 100644
--- a/arch/x86/include/asm/virtext.h
+++ b/arch/x86/include/asm/virtext.h
@@ -130,12 +130,4 @@ static inline void cpu_svm_disable(void)
}
}

-/** Makes sure SVM is disabled, if it is supported on the CPU
- */
-static inline void cpu_emergency_svm_disable(void)
-{
- if (cpu_has_svm(NULL))
- cpu_svm_disable();
-}
-
#endif /* _ASM_X86_VIRTEX_H */
diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
index 85ea1fdebf4c..3eec3cdbc054 100644
--- a/arch/x86/kernel/reboot.c
+++ b/arch/x86/kernel/reboot.c
@@ -787,7 +787,7 @@ void machine_crash_shutdown(struct pt_regs *regs)
}
#endif

-#if IS_ENABLED(CONFIG_KVM_INTEL)
+#if IS_ENABLED(CONFIG_KVM_INTEL) || IS_ENABLED(CONFIG_KVM_AMD)
/* RCU-protected callback to disable virtualization prior to reboot. */
static cpu_emergency_virt_cb __rcu *cpu_emergency_virt_callback;

@@ -823,7 +823,7 @@ void cpu_emergency_disable_virtualization(void)
{
lockdep_assert_irqs_disabled();

-#if IS_ENABLED(CONFIG_KVM_INTEL)
+#if IS_ENABLED(CONFIG_KVM_INTEL) || IS_ENABLED(CONFIG_KVM_AMD)
cpu_emergency_virt_cb *callback;

rcu_read_lock();
@@ -832,8 +832,6 @@ void cpu_emergency_disable_virtualization(void)
callback();
rcu_read_unlock();
#endif
- /* KVM_AMD doesn't yet utilize the common callback. */
- cpu_emergency_svm_disable();
}

#if defined(CONFIG_SMP)
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 46b658d0f46e..d56d5fe42262 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -38,6 +38,7 @@
#include <asm/spec-ctrl.h>
#include <asm/cpu_device_id.h>
#include <asm/traps.h>
+#include <asm/reboot.h>
#include <asm/fpu/api.h>

#include <asm/virtext.h>
@@ -565,6 +566,11 @@ void __svm_write_tsc_multiplier(u64 multiplier)
preempt_enable();
}

+static void svm_emergency_disable(void)
+{
+ cpu_svm_disable();
+}
+
static void svm_hardware_disable(void)
{
/* Make sure we clean up behind us */
@@ -5084,6 +5090,13 @@ static struct kvm_x86_init_ops svm_init_ops __initdata = {
.pmu_ops = &amd_pmu_ops,
};

+static void __svm_exit(void)
+{
+ kvm_x86_vendor_exit();
+
+ cpu_emergency_unregister_virt_callback(svm_emergency_disable);
+}
+
static int __init svm_init(void)
{
int r;
@@ -5097,6 +5110,8 @@ static int __init svm_init(void)
if (r)
return r;

+ cpu_emergency_register_virt_callback(svm_emergency_disable);
+
/*
* Common KVM initialization _must_ come last, after this, /dev/kvm is
* exposed to userspace!
@@ -5109,14 +5124,14 @@ static int __init svm_init(void)
return 0;

err_kvm_init:
- kvm_x86_vendor_exit();
+ __svm_exit();
return r;
}

static void __exit svm_exit(void)
{
kvm_exit();
- kvm_x86_vendor_exit();
+ __svm_exit();
}

module_init(svm_init)
--
2.39.0.rc0.267.gcb52ba06e7-goog